This isn't the first time I've heard these stories, but they mostly related to the differences in tension. I changed sewing machines part way through piecing a quilt - the first one I ever had professionally quilted. When I mentioned this to the quilter (a rather superior, intimidating woman) and said I hoped that it wouldn't make too much difference she stuck her nose in the air and said "if you keep a consistent quarter inch seam it doesn't make any difference"
I hope she reads this board!
I also think that the differing tensions on machines are bound to make a difference. And like many others, I have never, ever had a quarter-inch foot give me a quarter-inch seam - it's usually more like 5/16ths. to 3/8ths!